It is known that a dental surgeon frequently has to carry out various operations in the mouth of his patient consisting of cutting, molding or grinding the teeth. The dental surgeon practices this particularly for therapeutic odontological constructions which consist of dental obturations made with the use of amalgam, of gold, of resin, of ceramic or other material, for surgical therapeutic constructions which consist of emplacing implants under the periosteum and splints or intraosseous implants etc., for orthodontic or periodontal therapeutic constructions which consist of emplacing metal or other apparatus aimed at correcting the position of the teeth and for the construction of restorative prostheses such as crowns, bridges, inlay, and onlay or removable prostheses such as dentures and prostheses with mucous support or with corono-mucous insertions.
According to the prior art processes known up until now, prosthetic or therapeutic constructions are machined without provision of guidance for the machining tool or "freehand". Generally, this is started by making an impression in the patient's mouth of the organ or organs to be fitted. From this impression a positive model of the organ is made by molding. The accessories or construction are made on this positive model, either directly by fitting or indirectly by use of a wax model. This model makes it possible to make a mold by the lost wax molding process on which the prosthetist fabricates the final construction. All these operations give rise to a certain number of errors to which the prosthetist must adapt.
Thus, laboratory technicians are expected to have a high level of competence in making the wax model, especially for judging whether the thickness of the wax will be sufficient to withstand the forces developed in use by chewing.
European Pat. No. 0033,492 describes a technique for probing the contours of dental stumps of a plaster model so as to gather data which are subsequently recorded. This permits the prosthetist to refine the shapes and sizes of the prosthesis which he machines with the use of an automatic machine tool. For this purpose it is necessary to add corrections corresponding to the wall thickness to the values read on the plaster stump, but to avoid overcompensating, which would make the prosthesis oversized.
According to another prior art technique taught by Federal German Pat. No. 1,776,012, a plaster model is made immediately after the impression. The impression on the plaster model of the tooth to be crowned is then prepared. A stump is cut, the gingival shoulder of which is worked with great precision. Moreover a cutting guide is provided which makes it possible subsequently to cut the stump of the actual tooth to be crowned according to a profile corresponding to that of the plaster model. Unfortunately, it has been found that this technique does not insure, especially for the gingival shoulder, a sufficient precision of execution.
U.S. Pat. No. 4,182,312 describes a technique for making a detachable prosthesis. In this case the upper and lower dental arches as well as the gum tissues are probed. This makes it possible to record numerical positional values which are used to control an automatic machine for fabricating the prosthesis. Gathering these data requires the use of an apparatus including a guide arm which is connected to a probe arm having three devices for coding the numerical positional values measured in the three dimensions. If it is wished that the numerical values recorded with such a device be significant, the probing must be performed in a very large number of locational points. Moreover the absence of a mechanical pressure sensor interferes with the quality of the numerical values measured.
U.S. Pat. No. 3,861,044 describes a technique for installing an insert or inlay on a tooth. The dental surgeon cuts a cavity on the tooth of his patient in a freehand manner. This cavity is then photographed, measured and coded. From these coded values are derived the data serving for the control of the machine tool for making the inlay. The cut tooth is filled with wax and modeled in the mouth in relation to the original occlusion surface. Finally, this occlusion surface modeled in wax is recorded in the mouth using optoelectronic means. The coded values thus recorded are used to control a machine tool which automatically makes the inlay.
It is seen that none of these prior art processes makes it possible to carry out all of the operations automatically. In all cases an important step is performed manually, so that there is a possibility of errors.
The present invention has the aim of avoiding these disadvantages by achieving a process and a device which is easily used by the dental surgeon, while reducing the likelihood of errors to a greater degree.